"Fused" refers to a manufacturing process of refractory bricks. The batch materials are heated and melted in an electric arc furnace, and poured into a mold in a liquid state, and then solidified to achieve ceramic bonding. Compared with sintered bricks, it has the characteristics of compact structure, low porosity, high volume density, high mechanical strength and high temperature structure strength, and strong resistance to molten glass.
The main varieties in the current market are: fused mullite bricks, fused zirconia corundum bricks, fused chromium zirconium corundum bricks, fused quartz bricks, fused corundum bricks, etc.
Which type of those electric fused refractory materials is more suitable for use in glass melting furnaces?
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1.Fused mullite brick
Fused mullite bricks use high alumina bauxite as raw material, and mix different bauxite into mullite composition (3Al2O3·2SiO2, mass fractions are: Al2O372%, SiO228%). It melts at around 2300℃, is poured into a sand mould at 1850℃, and then annealed to relieve stress. The main crystal phases are mullite and corundum, and the glass phase is filled between the crystal phases. Its resistance to molten glass erosion is stronger than that of sintered refractories, but not as good as other fused refractories. Adding a small amount (7%-8.5%) of zirconium dioxide can make the mullite crystal smaller and the brick structure dense. The amount of mullite can be increased to 60%-70%, which relatively reduces the content of the glass phase and reduces the amount of the product. crack. Fused mullite bricks are gradually replaced by fused zirconium bricks.
2.Fused zirconia corundum brick
Fused zirconia corundum bricks are divided into three grades according to the content of ZrO2, and the corresponding grades are: AZS-33 (containing ZrO233%), AZS-36 (containing ZrO236%), AZS-41 (containing ZrO241%).
Fused cast AZS refrctory brick is based on zircon and industrial alumina as the main raw materials, and a small amount of zircon-rich sand (in order to increase the content of ZrO2), soda ash and borax are added. According to the different atmosphere during melting, there are two kinds of reduction melting method and oxidative melting method. At present, the oxidation method is the main method. The oxidation melting method can remove the pollution caused by the graphite electrode in the molten liquid, and the carbon content is low (0.005% 0.02%), can reduce the bubble content in the glass, and improve the quality of the glass liquid.
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The matters needing attention when using fused zirconia corundum bricks are as follows.
Irregular changes in thermal expansion
Fused zirconia corundum bricks are characterized by stable and dense structure and strong resistance to molten glass. It can be seen from the figure that there is abnormal expansion at 900-1200℃.
Electrical insulation
The electric insulation of fused zirconia corundum bricks is better, and it decreases with the increase of temperature. It can be seen that the electrode bricks can be used in the production of soda lime glass furnace. Zirconia corundum bricks.
Thermal conductivity
The thermal conductivity of fused zirconia corundum bricks is more than twice that of clay bricks. Therefore, when making pool wall tiles, the cooling air volume required near the liquid level should be twice as large as when using clay bricks as pool walls.
3.Fused corundum brick
Fused corundum bricks are made of high-purity alumina as raw material, and a small amount of soda ash is introduced, and it is melted at 2000-2200℃. The production process is similar to that of high-aluminum products. There are fused α-corundum bricks, fused α, β-corundum bricks, and fused β-corundum bricks. Fused α-corundum bricks are mainly suitable for melting borosilicate glass, opal glass and sulfate-containing melts. The composition of the fused α, β-corundum bricks contains only a small amount of glass phase, which will not ooze out during use, and has little pollution to the glass liquid. Direct contact with the glass liquid will not cause the glass liquid to be colored. It has good corrosion resistance and is glass melting. Ideal material for the wall of the kiln cooling part, the bottom of the kiln, and the flow trough of the float glass melting furnace. Fused corundum bricks are suitable for the upper structure of the working pool of the melting furnace and the combustion port at the rear of the melting zone and the breast wall and small furnace flat screed near it.
4. Fused chromium zirconium corundum brick
Add10%-30% Cr2O3 into AZS-33 bricks, and produce fused chromium-zirconium corundum bricks (abbreviated as AZCS bricks, French brand ER2161) by non-shrinkage pouring method. Both the skin and the interior of the brick are dark green. The brick contains 4.5% shrinkage cavities and no connected pores. Due to the formation of aluminum chromium spinel solid solution, the viscosity of the glass phase is increased, and the corrosion resistance of glass liquid is greatly improved. It is 3.4 times of fused AZS-33 brick and 2.6 times of fused AZS-41 brick.
The production process of fused quartz brick is the same as that of quartz glass. Using high-purity quartz sand (with SiO2 content above 99.5%) as raw material, adding a small amount of Na2O as a mineralizer, and melting it in a graphite resistance furnace (1750-1800°C). After melting, the whole piece of molten material is quickly taken out, rolled into bricks, and then machined after cooling in the air. The coefficient of thermal expansion is extremely small, and the thermal shock resistance is good. It has strong corrosion resistance to boron glass liquid, but it is not resistant to the erosion of soda lime silica glass liquid.
